Pipe Reynolds Number Calculator
Enter velocity, diameter and kinematic viscosity to compute the pipe-flow Reynolds number Re = v·D/ν.
Input Data
Results
At a glance:The Reynolds number Re = ρ·v·D/μ = v·D/ν compares inertial to viscous forces in pipe flow, with D the pipe diameter (the characteristic length for internal flow), v mean velocity and ν = μ/ρ kinematic viscosity. It predicts the flow regime: laminar for Re < ~2300, transitional 2300–4000, turbulent > ~4000 (exact thresholds depend on pipe roughness and inlet conditions). Laminar flow has the parabolic Hagen–Poiseuille profile and friction factor λ = 64/Re; turbulent flow has a flatter profile and higher friction. This tool computes Re = vD/ν and labels the regime.
Formula
Re = v·D/ν = ρ·v·D/μ
$$Re = \dfrac{v\,D}{\nu}$$How to Use
- Enter mean velocity v (m/s).
- Enter diameter D (m) and kinematic viscosity ν (m²/s).
- The calculator returns Re and the regime.
Case Studies
Water in a pipe
v = 1 m/s, D = 0.05 m, ν = 1e-6 m²/s.
Re = 1×0.05/1e-6 = 50000.
Turbulent (typical water supply).
FAQ
Why D and not radius?
For internal pipe flow the diameter is the natural characteristic length; the Reynolds number is defined with D (so thresholds ~2300/4000 are calibrated to D).
What changes at Re ~ 2300?
The flow becomes unstable and transitions from smooth laminar to turbulent, dramatically increasing mixing and friction.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.